Channel access method for very high throughput (vht) wireless local access network system and station supporting the channel access method

ABSTRACT

A method for transmitting data in a wireless communication system, the method includes transmitting, by a first station, a plurality of request to send (RTS) frames to a second station through a plurality of subchannels, each of the plurality of RTS frames being transmitted through a corresponding one of the plurality of subchannels, each of the plurality of subchannels having a 20 megahertz (MHz) bandwidth; receiving, by the first station, at least one clear to send (CTS) frame in response to at least one of the plurality of RTS frames from the second station through at least one idle subchannel of the plurality of subchannels; and transmitting, by the first station, a data frame to the second station after receiving the at least one CTS frame, wherein each of the plurality of RTS frames includes first channel information related to the plurality of subchannels.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is a Continuation of co-pending U.S. patent applicationSer. No. 15/357,438 filed on Nov. 21, 2016, which is a Continuation ofU.S. patent application Ser. No. 14/800,425 filed on Jul. 15, 2015 (nowU.S. Pat. No. 9,526,114 issued on Dec. 20, 2016), which is aContinuation of U.S. patent application Ser. No. 14/579,286 filed onDec. 22, 2014 (now U.S. Pat. Ser. No. 9,107,222 issued on Aug. 11,2015), which is a Continuation of U.S. patent application Ser. No.12/999,836 filed on Dec. 17, 2010 (now U.S. Pat. No. 8,989,158 issued onMar. 24, 2015), which is the National Phase of PCT InternationalApplication No. PCT/KR2009/003264 filed on Jun. 18, 2009, which claimsthe benefit under 35 U.S.C. §119(a) to Korean Patent Application No.10-2008-0057246 filed on Jun. 18, 2008, all of which are herebyexpressly incorporated by reference into the present application.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a wireless local access network (WLAN),and more particularly, to a channel access mechanism in a very highthroughput (VHT) WLAN system and a station supporting the channel accessmechanism.

Discussion of the Related Art

With the advancement of information communication technologies, variouswireless communication technologies have recently been developed. Amongthe wireless communication technologies, a wireless local access network(WLAN) is a technology whereby super high-speed Internet access ispossible in a wireless fashion in homes or businesses or in a regionproviding a specific service by using a portable terminal such as apersonal digital assistant (PDA), a laptop computer, a portablemultimedia player (PMP), etc.

Ever since the institute of electrical and electronics engineers (IEEE)802, i.e., a standardization organization for WLAN technologies, wasestablished in February 1980, many standardization works have beenconducted. In the initial WLAN technology, a frequency of 2.4 GHz wasused according to the IEEE 802.11 to support a data rate of 1 to 2 Mbpsby using frequency hopping, spread spectrum, infrared ray communication,etc. Recently, the WLAN technology can support a data rate of up to 54Mbps by using orthogonal frequency division multiplex (OFDM). Inaddition, the IEEE 802.11 is developing or commercializing standards ofvarious technologies such as quality of service (QoS) improvement,access point (AP) protocol compatibility, security enhancement, radioresource measurement, wireless access in vehicular environments, fastroaming, mesh networks, inter-working with external networks, wirelessnetwork management, etc.

In the IEEE 802.11, the IEEE 802.11b supports a data rate of up to 11Mbps by using a frequency band of 2.4 GHz. The IEEE 802.11acommercialized after the IEEE 802.11b uses a frequency band of 5 GHzinstead of the frequency band of 2.4 GHz and thus significantly reducesinfluence of interference in comparison with the very congestedfrequency band of 2.4 GHz. In addition, the IEEE 802.11a has improvedthe data rate to up to 54 Mbps by using the OFDM technology.Disadvantageously, however, the IEEE 802.11a has a shorter communicationdistance than the IEEE 802.11b. Similarly to the IEEE 802.11b, the IEEE802.11g realizes the data rate of up to 54 Mbps by using the frequencyband of 2.4 GHz. Due to its backward compatibility, the IEEE 802.11g isdrawing attention, and is advantageous over the IEEE 802.11a in terms ofthe communication distance.

The IEEE 802.11n is a technical standard relatively recently introducedto overcome a limited data rate which has been considered as a drawbackin the WLAN. The IEEE 802.11n is devised to increase network speed andreliability and to extend an operational distance of a wireless network.More specifically, the IEEE 802.11n supports a high throughput (HT),i.e., a data processing speed of up to 540 Mbps at a frequency band of 5GHz, and is based on a multiple input and multiple output (MIMO)technique which uses multiple antennas in both a transmitter and areceiver to minimize a transmission error and to optimize a data rate.In addition, this standard may use a coding scheme which transmitsseveral duplicated copies to increase data reliability and also may usethe OFDM to support a higher data rate.

Meanwhile, a basic access mechanism of an IEEE 802.11 medium accessmechanism (MAC) is a carrier sense multiple access with collisionavoidance (CSMA/CA) combined with binary exponential backoff. TheCSMA/CA mechanism is also referred to as a distributed coordinatefunction (DCF) of the IEEE 802.11 MAC, and basically employs a “listenbefore talk” access mechanism. In this type of access mechanism, astation (STA) listens a wireless channel or medium before startingtransmission. As a result of listening, if it is sensed that the mediumis not in use, a listening STA starts its transmission. Otherwise, if itis sensed that the medium is in use, the STA does not start itstransmission but enters a delay duration determined by the binaryexponential backoff algorithm.

The CSMA/CA mechanism also includes virtual carrier sensing in additionto physical carrier sensing in which the STA directly listens themedium. The virtual carrier sensing is designed to compensate for alimitation in the physical carrier sensing such as a hidden nodeproblem. For the virtual carrier sending, the IEEE 802.11 MAC uses anetwork allocation vector (NAV). The NAV is a value transmitted by anSTA, currently using the medium or having a right to use the medium, toanther STA to indicate a remaining time before the medium returns to anavailable state. Therefore, a value set to the NAV corresponds to aduration reserved for the use of the medium by an STA transmitting acorresponding frame.

One of procedures for setting the NAV is a exchange procedure of arequest to send (RTS) frame and a clear to send (CTS) frame. The RTSframe and the CTS frame include information capable of delayingtransmission of frames from receiving STAs by reporting upcoming frametransmission to the receiving STAs. The information may be included in aduration filed of the RTS frame and the CTS frame. After performing theexchange of the RTS frame and the CTS frame, a source STA transmits ato-be-transmitted frame to a destination STA.

FIG. 1 is a diagram showing an IEEE 802.11 MAC architecture including aDCF. Referring to FIG. 1, a service of the DCF is used to provide apoint coordination function (PCF) and a hybrid coordination function(HCF). The HCF includes an enhanced distributed channel access (EDCA)and an HCF controller channel access (HCCF). The HCF does not exist inan STA not supporting quality of service (QoS). On the other hand, boththe DCF and the HCF exist in an STA supporting QoS. The PCF is anarbitrary function in all STAs. Details of the DCF, PCF, EDCA, and HCCFare disclosed in section 9 of the “MAC sublayer function description” inthe IEEE 802.11-REVma/D9.0 October 2006 standard, and thus descriptionsthereof will be omitted herein. The contents of the above standard areincorporated herein by reference.

With the widespread use of WLAN and the diversification of applicationsusing the WLAN, there is a recent demand for a new WLAN system tosupport a higher throughput than a data processing speed supported bythe IEEE 802.11n. However, an IEEE 802.11n medium access control(MAC)/physical layer (PHY) protocol is not effective to provide athroughput of 1 Gbps or more. This is because the IEEE 802.11n MAC/PHYprotocol is designed for an operation of a single STA, that is, an STAhaving one network interface card (NIC), and thus when a framethroughput is increased while maintaining the conventional IEEE 802.11nMAC/PHY protocol, a resultant additional overhead is also increased.Consequently, there is a limitation in increasing a throughput of awireless communication network while maintaining the conventional IEEE802.11n MAC/PHY protocol, that is, a single STA architecture.

Therefore, to achieve a data processing speed of 1 Gbps or more in thewireless communication system, a new system different from theconventional IEEE 802.11n MAC/PHY protocol (i.e., single STAarchitecture) is required. A very high throughput (VHT) system is a nextversion of the IEEE 802.11n WLAN system, and is one of IEEE 802.11 WLANsystems which have recently been proposed to support a data processingspeed of 1 Gbps or more in a MAC service access point (SAP). The VHTsystem is named arbitrarily. To provide a throughput of 1 Gbps or more,a feasibility test is currently being conducted for the VHT system using4×4 MIMO and a channel bandwidth of 80 MHz.

Meanwhile, a data processing speed of 1 Gbps or more, which is set as atarget throughput in a VHT system, denotes an aggregate throughput. Onthe other hand, a target throughput in one-to-one communication betweenSTAs is at least 500 Mbps in the VHT system. This implies thatperformance or an offered load of an STA supporting VHT (hereinafter,simply referred to as a ‘VHT STA’) may not exceed 500 Mbps. In a casewhere the offered load of the VHT STA is less than 1 Gbps (e.g., 500Mbps), the target throughput of the VHT system cannot be achieved whenone VHT STA is allowed to use an entire channel similarly to theconventional channel access method.

In addition, there is a problem in that efficiency is not high in theaforementioned CSMA/CA channel access method used in the IEEE 802.11WLAN. For example, a data processing speed in a MAC SAP is only 50 to60% of a data processing speed in a PHY SAP. Therefore, in order toachieve a data processing speed of 1 Gbps or more in the MAC SAP of theVHT system, the data processing speed of the PHY SAP needs to be about1.5 to 2 times higher than 1 Gbps. However, the conventional IEEE802.11n PHY technique has difficulty in providing such a processingspeed.

SUMMARY OF THE INVENTION

The present invention provides a new channel access method for achievingan aggregate throughput of 1 Gbps or more in a very high throughput(VHT) system.

The present invention also provides a channel access method for allowingsimultaneous channel access of a plurality of VHT stations (STAs) in aVHT system.

The present invention also provides a new channel access method forachieving an aggregate throughput of 1 Gbps or more in a medium accesscontrol (MAC) service access point (SAP) in a VHT system.

According to an aspect of the present invention, there is provided achannel access method in a very high throughput (VHT) system using abonding channel consisting of a plurality of subchannels, comprising:transmitting a request to send (RTS) frame by one source station or eachof a plurality of source stations to a destination station through anysubchannel selected from the plurality of subchannels; and in responseto the received RTS frame, transmitting a clear to send (CTS) frame bythe destination station to one source station selected from theplurality of source stations through the bonding channel.

According to another aspect of the present invention, there is provideda channel access method in a very high throughput (VHT) system using abonding channel consisting of a plurality of subchannels, comprising:transmitting a request to send (RTS) frame by a source station to adestination station for each of the plurality of subchannels; andtransmitting a clear to send (CTS) frame by the destination station tothe source station through a subchannel in which the RTS frame issuccessfully received.

According to still another aspect of the present invention, there isprovided a channel access method in a very high throughput (VHT) systemusing a bonding channel consisting of a plurality of subchannels,comprising: transmitting a request to send (RTS) frame by one sourcestation or each of a plurality of source stations to a destinationstation through any subchannel selected from the plurality ofsubchannels; and in response to the received RTS frame, transmitting aclear to send (CTS) frame by the destination station to one sourcestation selected from the plurality of source stations through thebonding channel, wherein the CTS frame comprises a list of subchannelsto be used by the source station that receives the CTS frame to transmita subsequent frame.

According to still another aspect of the present invention, there isprovided a channel access method in a very high throughput (VHT) systemusing a bonding channel consisting of a plurality of subchannels,wherein a source station transmits a request to send (RTS) frame to adestination station by using any subchannel among the plurality ofsubchannels or by using each of the plurality of subchannels.

According to still another aspect of the present invention, there isprovided a channel access method in a very high throughput (VHT) systemusing a bonding channel consisting of a plurality of subchannels,wherein a request to send (RTS) frame transmitted by a source station toa destination station comprises a list of subchannels which are desiredto be used by the source station among the plurality of subchannels totransmit a subsequent frame.

According to still another aspect of the present invention, there isprovided a channel access method in a very high throughput (VHT) systemusing a bonding channel consisting of a plurality of subchannels,wherein a clear to send (CTS) frame transmitted by a destination stationto a receiving station in response to a received request to send (RTS)frame comprises a list of subchannels which are allowed to be used bythe source station among the plurality of subchannels to transmit asubsequent frame.

An effective channel access mechanism is provided to improve usageefficiency of a bonding channel consisting of a plurality of subchannelsin a very high throughput (VHT) system using the bonding channel. Inparticular, according to an embodiment of the present invention, accessto another subchannel is allowed not only in a case where one or moreVHT stations simultaneously request channel access but also in a casewhere some of subchannels are used by a legacy station, thereby enablingeffective channel access.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing an institute of electrical and electronicsengineers (IEEE) 802.11 medium access control (MAC) architectureincluding a distributed coordinate function (DCF).

FIG. 2 is a schematic view showing an exemplary structure of a wirelesslocal access network (WLAN) system according to an embodiment of thepresent invention.

FIG. 3 is a block diagram showing a multi-radio unification protocol(MUP) as an example of a protocol applicable to a very high throughput(VHT) system including a plurality of network interface cards (NICs)each having an independent radio interface.

FIG. 4 is a diagram showing a channel access mechanism according to afirst embodiment of the present invention.

FIG. 5 is a diagram showing a channel access mechanism according to asecond embodiment of the present invention.

FIG. 6 is a diagram showing a channel access mechanism according to athird embodiment of the present invention.

FIG. 7 is a diagram showing a channel access mechanism according to afourth embodiment of the present invention.

FIG. 8 is a diagram showing a channel access mechanism according to afifth embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 2 is a schematic view showing an exemplary structure of a wirelesslocal access network (WLAN) system according to an embodiment of thepresent invention.

Referring to FIG. 2, the WLAN system includes one or more basis servicesets (BSSs). The BSS is a set of stations (STAs) which are successfullysynchronized to communicate with one another, and is not a conceptindicating a specific region. A very high throughput (VHT) BSS isdefined as a BSS that supports a super high-speed data processing speedof 1 GHz or more.

A VHT system including one or more VHT BSSs can use a channel bandwidthof 80 MHz, which is for exemplary purposes only. For example, the VHTsystem may use a channel bandwidth of 60 MHz or 100 MHz or more. Assuch, the VHT system operates in a multi-channel environment where aplurality of subchannels having a specific size, e.g., a channelbandwidth of 20 MHz, are included.

The BSS can be classified into an infrastructure BSS and an independentBSS (IBSS). The infrastructure BSS is shown in FIG. 2. InfrastructureBSSs (i.e., BSS1 and BSS2) include one or more STAs (i.e., STA1, STA3,and STA4), access points (APs) which are STAs providing a distributionservice, and a distribution system (DS) connecting a plurality of APs(i.e., AP1 and AP2). On the other hand, the IBSS does not include APs,and thus all STAs are mobile STAs. In addition, the IBSS constitutes aself-contained network since connection to the DS is not allowed.

The STA is an arbitrary functional medium including a medium accesscontrol (MAC) and wireless-medium physical layer (PHY) interfaceconforming to the institute of electrical and electronics engineers(IEEE) 802.11 standard, and includes both an AP and a non-AP STA in abroad sense. A VHT STA is defined as an STA that supports the superhigh-speed data processing speed of 1 GHz or more in the multi-channelenvironment to be described below.

The STA for wireless communication includes a processor and atransceiver, and also includes a user interface, a display element, etc.The processor is a functional unit devised to generate a frame to betransmitted through a wireless network or to process a frame receivedthrough the wireless network, and performs various functions to controlSTAs. The transceiver is functionally connected to the processor and isa functional unit devised to transmit and receive a frame for the STAsthrough the wireless network.

Among the STAs, non-AP STAs (i.e., STA1, STA3, STA4, STA6, STA7, andSTA8) are portable terminals operated by users. A non-AP STA may besimply referred to as an STA. The non-AP STA may also be referred to asa wireless transmit/receive unit (WTRU), a user equipment (UE), a mobilestation (MS), a mobile terminal, a mobile subscriber unit, etc. A non-APVHT-STA is defined as a non-AP STA that supports the super high-speeddata processing speed of 1 GHz or more in the multi-channel environmentto be described below.

The AP (i.e., AP1 and AP2) is a functional entity for providingconnection to the DS through a wireless medium for an associated STA.Although communication between non-AP STAs in an infrastructure BSSincluding the AP is performed via the AP in principle, the non-AP STAscan perform direct communication when a direct link is set up. Inaddition to the terminology of an access point, the AP may also bereferred to as a centralized controller, a base station (BS), a node-B,a base transceiver system (BTS), a site controller, etc. A VHT AP isdefined as an AP that supports the super high-speed data processingspeed of 1 GHz or more in the multi-channel environment to be describedbelow.

A plurality of infrastructure BSSs can be interconnected by the use ofthe DS. An extended service set (ESS) is a plurality of BSSs connectedby the use of the DS. STAs included in the ESS can communicate with oneanother. In the same ESS, a non-AP STA can move from one BSS to anotherBSS while performing seamless communication.

The DS is a mechanism whereby one AP communicates with another AP. Byusing the DS, an AP may transmit a frame for STAs associated with a BSSmanaged by the AP, or transmit a frame when any one of the STAs moves toanother BSS, or transmit a frame to an external network such as a wirednetwork. The DS is not necessarily a network, and has no limitation inits format as long as a specific distribution service specified in theIEEE 802.11 can be provided. For example, the DS may be a wirelessnetwork such as a mesh network, or may be a physical structure forinterconnecting APs.

FIG. 3 is a block diagram showing a multi-radio unification protocol(MUP) as an example of a protocol applicable to a VHT system including aplurality of network interface cards (NICs) each having an independentradio interface.

Referring to FIG. 3, an STA supporting the MUP includes a plurality ofNICs. The NICs are separately depicted in FIG. 3, which implies thateach NIC independently operates a MAC/PHY module. That is, the NICs aredistinctively depicted in FIG. 3 to show that the NICs are logicalentities operating according to individual MAC/PHY protocols. Therefore,the plurality of NICs can be implemented with physically distinctivefunctional entities, or can be implemented by integrating the physicalentities into one physical entity.

According to one aspect of the present embodiment, the plurality of NICscan be classified into a primary radio interface and one or moresecondary radio interfaces. If a plurality of secondary radio interfacesare present, the secondary radio interfaces can be classified into afirst secondary radio interface, a second secondary radio interface, athird secondary radio interface, etc. The classification into theprimary interface and the secondary interface and/or the classificationof the secondary ratio interface itself may be determined by a policy ormay be adoptively determined in consideration of a channel environment.

The plurality of NICs are integrally managed according to the MUP. As aresult, the plurality of NICs are externally recognized as if they areone device. For this, the VHT system includes a virtual-MAC (V-MAC).Through the V-MAC, an upper layer cannot recognize that a multi-radiochannel is operated by the plurality of NICs. As such, in the VHTsystem, the upper layer does not recognize the multi-radio channelthrough the V-MAC. This means that one virtual Ethernet address isprovided.

Next, a channel allocation mechanism in a VHT system will be describedaccording to embodiments of the present invention. Although theembodiments described below relate to a VHT system using a bondingchannel in which contiguous 4 subchannels having a bandwidth of 20 MHzare combined (i.e., a bonding channel having a channel bandwidth of 80MHz), this is for exemplary purposes only. The embodiments describedbelow can equally apply to a VHT system including a plurality ofsubchannels (e.g., 3 or 5 or more subchannels), which is apparent tothose skilled in the art. In addition, the embodiments of the presentinvention are not limited to the VHT system whose subchannel has abandwidth of 20 MHz.

FIG. 4 is a diagram showing a channel access mechanism in a VHT WLANsystem according to a first embodiment of the present invention. In thepresent embodiment, the conventional channel access mechanism (e.g.,enhanced distributed channel access (EDCA) mechanism) is directly usedfor an entire bonding channel, and it is assumed that a full channelbandwidth is used by only one VHT STA. That is, the entire bondingchannel is used to exchange a request to send (RTS) frame, a clear tosend (CTS) frame, and data between two VHT STAB performing communicationwith each other.

Referring to FIG. 4, a source VHT STA or a transmitting VHT STA, whichintends to transmit data, transmits an RTS frame by using the entirebonding channel. In FIG. 4, a process of transmitting the RTS frame isindicated by a physical layer convergence procedure (PLCP) preamble, aPLCP header, and a single PLCP protocol data unit (PPDU).

Upon receiving the RTS frame, a destination VHT STA or a receiving VHTSTA transmits a CTS frame also by using the entire bonding channel. InFIG. 4, a process of transmitting the CTS frame is also indicated by aPLCP preamble, a PLCP header, and a single PPDU.

When the RTS frame and the CTS frame are exchanged by using the entirebonding channel, subsequent data or the like is generally transmittedalso by using the entire bonding channel. However, according to anaspect of the present embodiment, the RTS frame and/or the CTS frame mayinclude a list of subchannels to be used for transmission of subsequentdata or the like. As such, when the RTS frame and/or the CTS frameinclude the list of subchannels, a network allocation vector (NAV) isset only for a specific subchannel included in the list, and the sourceVHT STA transmits the data or the like to the destination VHT STA onlythrough the specific subchannel.

Consequently, upon receiving the CTS frame, the source VHT STA startstransmission of the data or the like to the destination VHT STAaccording to a predetermined procedure. In FIG. 4, a process oftransmitting the data is also indicated by a PLCP preamble, a PLCPheader, and a single PPDU. In this case, if the list of subchannels doesnot exist in the RTS frame and/or the CTS frame, as shown in FIG. 4, thedata or the like is transmitted by using the entire bonding channel.Otherwise, if the list of subchannels exists, the data or the like maybe transmitted by using all or some of subchannels included in the list.

As described above, according to the first embodiment of the presentinvention, the RTS frame, the CTS frame, the data frame, etc., aretransmitted through the entire bonding channel directly using thechannel access mechanism based on the conventional EDCA. As amodification of the first embodiment, a list of subchannels to be usedfor transmission of the data frame or the like may be included in theRTS frame and/or the CTS frame. If the list of subchannels is included,the source VHT STA can transmit the data frame or the like to thedestination VHT STA by using all or some of subchannels of the list.

In a case where the RTS frame and the CTS frame are transmitted by usingthe entire bonding channel, the RTS frame and the CTS frame are verysmall in size, and thus a transmission time corresponds to only a feworthogonal frequency division multiplex (OFDM) symbols (e.g., 8 ?srequired for transmission of 6 Mbs). Optionally, the transmission timeof the RTS frame and the CTS frame may be less than the PLCP preambleand the PLCP header. A network overhead for the RTS frame and the CTSframe is almost negligible.

FIG. 5 is a diagram showing a channel access mechanism in a VHT WLANsystem according to a second embodiment of the present invention. Thepresent embodiment is an example of a channel access mechanism forsolving a problem of collision with a legacy STA in a VHT system inwhich a VHT STA coexists with the legacy STA, when the conventional EDCAchannel access mechanism is used as in the first embodiment describedabove. Such a channel access mechanism can also be referred to as, forexample, frequency-selective EDCA.

According to the aforementioned first embodiment, an entire bondingchannel cannot be used when the collision with the legacy STA occurs,which may result in significant throughput deterioration of the VHTsystem. If the VHT STA is in use or one or more legacy STAs operates inany subchannel among subchannels to be used, in order for the VHT STA toaccess to a channel including the subchannel or to access to the entirebonding channel, all subchannels constituting the channel or the bondingchannel have to be unoccupied (or idle). That is, the VHT STA cansuccessfully perform channel access only when the collision with thelegacy STA does not occur with respect to all subchannels constitutingthe bonding channel.

According to the present embodiment, a channel access mechanism fortransmitting an RTS frame for each subchannel is used to prevent aproblem of throughput deterioration caused by the collision with thelegacy STA. That is, a source VHT STA transmits the RTS frame for eachsubchannel instead of transmitting the RTS frame by using the entirebonding channel. If collision occurs with the legacy STA in anysubchannel while the RTS frame for each subchannel is transmitted, adestination VHT STA transmits a CTS frame only for a subchannel in whichno collision occurs, and as a result, the source VHT STA receives theCTS frame only for the subchannel in which no collision occurs. Further,the source VHT STA transmits data or the like only for a subchannel inwhich the CTS frame is received.

Referring to FIG. 5, the source VHT STA or the transmitting VHT STA(indicated by ‘STA1’ in FIG. 5), which intends to transmit data,transmits an RTS frame by using the entire bonding channel. In thepresent embodiment, the RTS frame is transmitted for each subchannel byregarding each subchannel as an independent channel, instead ofregarding the entire bonding channel as one channel. In FIG. 5, aprocess of transmitting the RTS frame for each subchannel is indicatedby a PLCP preamble, a PLCP header, and a single PPDU for eachsubchannel.

However, according to the present embodiment, among all subchannels, a2nd subchannel and a 4th subchannel are used by the legacy STA. The 2ndsubchannel and the 4th subchannel may be in use by different legacySTAs. Although the 2nd subchannel and the 4th subchannel are used by thelegacy STA herein, this is for exemplary purposes only, and thus theembodiment of the present invention is not limited thereto. If the 2ndsubchannel and the 4th subchannel are already being used, RTS framestransmitted through these subchannels may be unsuccessfully transmitteddue to collision, and a destination VHT STA may successfully receive RTSframes transmitted through a 1st subchannel and a 3rd subchannel.

Upon receiving the RTS frames through all or some of subchannels, thedestination VHT STA or the receiving VHT STA transmits a CTS frame foreach subchannel by using corresponding subchannels. In FIG. 5, a processof transmitting the CTS frame is indicated by a PLCP preamble, a PLCPheader, and a single PPDU in the 1st and 3rd subchannels.

Upon receiving the CTS frame through the 1st and 3rd subchannels, thesource VHT STA transmits data or the like by using correspondingsubchannels (i.e., the 1st and 3rd subchannels). In FIG. 5, a process oftransmitting the data through the 1st and 3rd subchannels is indicatedby a PLCP preamble, a PLCP header, and a single PPDU in the 1st and 3rdsubchannels.

FIG. 6 is a diagram showing a channel access mechanism in a VHT WLANsystem according to a third embodiment of the present invention. Thepresent embodiment is an example of a channel access mechanism forpreventing collision between VHT STAB in a VHT system in which the VHTSTA coexists with a legacy STA or in a VHT BSS in which only the VHT STAexists. Such a channel access mechanism can also be referred to as, forexample, frequency-hopping EDCA.

According to the aforementioned first embodiment, if the legacy STAoccupies any one subchannel at a time for transmitting an RTS frame, theVHT STA cannot immediately transmit data or the like by using an entirebonding channel even after the use of the subchannel is finished. Thatis, only after the legacy STA finishes the use of the subchannel, aprocedure of exchanging the RTS frame and a CTS frame can begin.According to the aforementioned second embodiment, the entire bondingchannel cannot be used for transmission of data or the like whencollision occurs with the legacy STA, and thus there is a disadvantagein that a throughput of the VHT system deteriorates.

According to the present embodiment, a channel access mechanism in whichone VHT STA transmits an RTS frame by using only one subchannel is usedto prevent a problem of transmission delay on data or the like, whichmay be caused in the first embodiment, or a problem of deterioration inchannel usage efficiency, which may be caused in the second embodiment.More specifically, each VHT STA intending to transmit data or the liketransmits an RTS frame by selecting any one subchannel or by using onlyone subchannel according to a predetermined rule, instead oftransmitting the RTS frame by using the entire bonding channel. That is,each VHT STA performs channel access by using an EDCA scheme throughselected or predetermined one subchannel. As such, according to thepresent embodiment, RTS frames are transmitted by using only onesubchannel, and thus even if a plurality of VHT STAs simultaneouslytransmit the RTS frames, collision between the RTS frames can beprevented or avoided.

Upon receiving the RTS frames from one or more VHT STAs, a destinationVHT STA or a receiving VHT STA transmits a CTS frame as a response byselecting one of the received RTS frames, that is, by selecting one VHTSTA from the VHT STAs transmitting the RTS frames. In this case, the CTSframe can be transmitted through the entire bonding channel or, as inthe aforementioned second embodiment, can be transmitted for eachcorresponding subchannel. In the latter case, the CTS frame istransmitted for each subchannel through the entire bonding channelinstead of using only a subchannel identical to the subchannel in whichthe selected RTS frame is transmitted. In addition, according to thepresent embodiment, the VHT STA which has received the CTS frame, i.e.,the destination VHT STA of the CTS frame, uses the entire bondingchannel when intending to transmit data or the like in a subsequentprocedure.

Referring to FIG. 6, source VHT STAs or transmitting VHT STAs (indicatedby ‘STA1’ and ‘STA2’ in FIG. 6), which intend to transmit data, transmitRTS frames through any respective subchannels. For example, this may bea case where backoff timers of the STA1 and the STA2 are simultaneouslyexpired. It is shown in FIG. 6 that the STA1 uses a 1st subchannel andthe STA2 uses a 3rd subchannel, which is for exemplary purposes only.According to the present embodiment, preferably, the STA1 and the STA2transmit the RTS frames by using different subchannels, and thesubchannels can be determined without any restriction. When the STA1 andthe STA2 transmit the RTS frames by using different subchannels,collision between the RTS frames can be prevented. In FIG. 6, a processof transmitting the respective RTS frames by the STA1 and the STA2through the different subchannels is indicated by a PLCP preamble, aPLCP header, and a single PPDU in the 1st and 3rd subchannels.

When the destination VHT STA or the receiving VHT STA receives separateRTS frames through 1st and 3rd subchannels among all subchannels, thedestination VHT STA or the receiving VHT STA transmits a CTS frame as aresponse by selecting only one RTS frame. It is shown in FIG. 6 that anRTS frame received from the 1st VHT STA (i.e., STA1) is selected andthus the CTS frame is transmitted to the STA1, which is for exemplarypurposes only. In addition, according to the present embodiment, the CTSframe is transmitted through the entire bonding channel. In FIG. 6, aprocess of transmitting the CTS frame is indicated by a PLCP preamble, aPLCP header, and a single PPDU in the entire bonding channel, and theCTS frame is transmitted to the STA1.

Upon receiving the CTS frame, the STA1 transmits data or the like byusing the entire bonding channel. Therefore, according to the presentembodiment, channel usage efficiency can be maximized when transmittingdata of the like. In FIG. 6, a process of transmitting the data throughall subchannels is indicated by a PLCP preamble, a PLCP header, and asingle PPDU in the entire bonding channel.

As described in the aforementioned second embodiment and in the presentembodiment, if an RTS frame and/or a CTS frame are transmitted by usingonly one subchannel, a transmission time of the RTS frame and the CTSframe is relatively increased. However, since the RTS frame is small insize, a transmission overhead of the RTS frame is not relatively large.On the other hand, according to the present embodiment, RTS frames aretransmitted by using only one subchannel, and thus collision between theRTS frames can be prevented. As a result, according to the presentembodiment, a possibility of collision between VHT STAB can be reduced,and thus channel usage efficiency can also be increased to that extent.

FIG. 7 is a diagram showing a channel access mechanism in a VHT WLANsystem according to a fourth embodiment of the present invention. Thatis, as in the third embodiment, the present embodiment also uses thefrequency-hopping EDCA. However, in the present invention, a CTS frameis transmitted in a different manner from that described in the thirdembodiment. The following description will focus on different aspectsfrom the third embodiment.

It is assumed in the aforementioned third embodiment that only a VHT STAperforms channel access. In this case, there is no need to consider NAVsetting in a legacy STA. Therefore, in the aforementioned thirdembodiment, a CTS frame is transmitted through an entire bonding channelwhen the CTS frame is transmitted. By transmitting the CTS frame in sucha manner, a channel load caused by transmission of the CTS frame can bereduce. However, if the CTS frame is transmitted through the entirebonding channel, the legacy STA cannot decode the CTS frame, and thuscannot set the NAV during a time period determined by the CTS frame.Accordingly, in the present embodiment, the CTS frame is transmitted byusing one subchannel.

According to another aspect of the present embodiment, as described inthe third embodiment, the CTS frame may be transmitted for eachsubchannel constituting the bonding channel. In this case, the CTS framemay include a subchannel list for indicating a specific subchannel forwhich each VHT STA has a transmission opportunity. For example, iftransmission is allowed for one VHT STA, a list of subchannels that canbe used by the VHT STA may be included in the CTS frame. Alternatively,if no subchannel list is included, the VHT STA may have a transmissionopportunity for all subchannels.

FIG. 8 is a diagram showing a channel access mechanism in a VHT WLANsystem according to a fifth embodiment of the present invention. Thepresent embodiment is an example of a channel access mechanism forpreventing collision between VHT STAs in a VHT system in which the VHTSTA coexists with a legacy STA or in a VHT BSS in which only the VHT STAexists. The present embodiment can be regarded as an application of theaforementioned third and fourth embodiments. Such a channel accessmechanism can also be referred to as, for example, frequency-hoppingEDCA with dynamic channel allocation.

As in the third embodiment and the fourth embodiment, according to thechannel access mechanism using the frequency-hopping EDCA, a destinationVHT STA can simultaneously receive RTS frames from a plurality of UEs orcan receive an additional RTS frame through an unused subchannel. Inthis case, the present embodiment allows several UEs to simultaneouslytransmit data or the like through different subchannels by respectivelytransmitting CTS frames to one or more UEs which have received the RTSframes. The CTS frame includes a list of subchannels to be used when acorresponding UE transmits data or the like.

Referring to FIG. 8, source VHT STAs or transmitting VHT STAs (indicatedby ‘STA1’ and ‘STA2’ in FIG. 8), which intend to transmit data, transmitRTS frames through any respective subchannels. For example, this may bea case where backoff timers of the STA1 and the STA2 are simultaneouslyexpired. It is shown in FIG. 8 that, to transmit an RTS frame, the STA1uses a 1st subchannel and the STA2 uses a 3rd subchannel, which is forexemplary purposes only. According to the present embodiment,preferably, the STA1 and the STA2 transmit the RTS frames by usingdifferent subchannels, and the subchannels can be determined without anyrestriction. When the STA1 and the STA2 transmit the RTS frames by usingdifferent subchannels, collision between the RTS frames can beprevented. In FIG. 8, a process of transmitting the respective RTSframes by the STA1 and the STA2 through the different subchannels isindicated by a PLCP preamble, a PLCP header, and a single PPDU in the1st and 3rd subchannels.

When the destination VHT STA or the receiving VHT STA receives separateRTS frames through 1st and 3rd subchannels among all subchannels, thedestination VHT STA or the receiving VHT STA transmits a CTS frame as aresponse with respect to all received RTS frames. It is shown in FIG. 8that two CTS frames are respectively transmitted to the STA1 and theSTA2 through the 1st and 3rd subchannels for the respective RTS framesreceived from the STA1 and the STA2. In FIG. 8, a process oftransmitting the CTS frame is indicated by a PLCP preamble, a PLCPheader, and a single PPDU in each of the 1st and 3rd subchannels.

According to the present embodiment, a list of subchannels to be used bythe STA1 to transmit subsequent data or the like is included in a CTSframe to be transmitted to the STA1. According to the present invention,1st and 2nd subchannels are included in the list, which is for exemplarypurpose only. In addition, the list of subchannels to be used by theSTA2 to transmit subsequent data or the like is also included in a CTSframe to be transmitted to the STA2. According to the presentembodiment, 3rd and 4th subchannels are included in the list, which isfor exemplary purpose only.

Upon receiving the CTS frame, each of the STA1 and the STA2 transmitsdata or the like to the destination STA through a subchannel included inthe subchannel list of the received CTS frame. The STA1 and the STA2 cansimultaneously transmit the data or the like. In FIG. 8, a process oftransmitting the data through 1st and 2nd subchannels of the 1st VHT STAand transmitting the data through 1st and 2nd subchannels of the 2nd VHTSTA is indicated by a PLCP preamble, a PLCP header, and a single PPDU inthe 1st and 2nd subchannels and the 3rd and 4th subchannels.

According to the embodiment of the present invention, a plurality of VHTSTAs or a VHT STA and a legacy STA can transmit data or the like byusing an entire bonding channel. In addition, according to theembodiment of the present invention in which a CTS frame includes a listof subchannels to be used, a VHT STA for using each subchannel can beadaptively determined by considering all conditions at the request of aplurality of VHT STAs. Therefore, according to the present embodiment,channel usage efficiency can be improved when transmitting data or thelike.

What is claimed is:
 1. A method for transmitting data in a wirelesscommunication system, the method comprising: transmitting, by a firststation, a plurality of request to send (RTS) frames to a second stationthrough a plurality of subchannels, each of the plurality of RTS framesbeing transmitted through a corresponding one of the plurality ofsubchannels, each of the plurality of subchannels having a 20 megahertz(MHz) bandwidth; receiving, by the first station, at least one clear tosend (CTS) frame in response to at least one of the plurality of RTSframes from the second station through at least one idle subchannel ofthe plurality of subchannels; and transmitting, by the first station, adata frame to the second station after receiving the at least one CTSframe, wherein each of the plurality of RTS frames includes firstchannel information related to the plurality of subchannels, wherein theat least one CTS frame includes second channel information related tothe at least one idle subchannel through which the at least one CTSframe is received by the first station and the data frame is transmittedthrough the at least one idle subchannel indicated by the second channelinformation, and wherein a number of the at least one idle subchannelthrough which the at least one CTS frame is received is equal to or lessthan a number of the plurality of subchannels through which theplurality of RTS frames are transmitted.
 2. The method of claim 1,wherein the number of the at least one idle subchannel is 1, 2 or 4 whenthe number of the plurality of subchannels is
 4. 3. The method of claim1, wherein the number of the at least one idle subchannel is 1 or 2 whenthe number of the plurality of subchannels is
 2. 4. The method of claim1, wherein the first station is a Very High Throughput (VHT) non-AccessPoint (AP) station and the second station is a VHT AP station.
 5. Adevice comprising: a transceiver; and a processor operatively connectedto the transceiver and configured to: instruct the transceiver totransmit a plurality of request to send (RTS) frames to a stationthrough a plurality of subchannels, each of the plurality of RTS framesbeing transmitted through a corresponding one of the plurality ofsubchannels, each of the plurality of subchannels having a 20 megahertz(MHz) bandwidth, instruct the transceiver to receive at least one clearto send (CTS) frame in response to at least one of the plurality of RTSframes from the station through at least one idle subchannel of theplurality of subchannels, and instruct the transceiver to transmit adata frame to the station after receiving the at least one CTS frame,wherein each of the plurality of RTS frames includes first channelinformation related to the plurality of subchannels, wherein the atleast one CTS frame includes second channel information related to theat least one idle subchannel through which the at least one CTS frame isreceived by the device and the data frame is transmitted through the atleast one idle subchannel indicated by the second channel information,and wherein a number of the at least one idle subchannel through whichthe at least one CTS frame is received is equal to or less than a numberof the plurality of subchannels through which the plurality of RTSframes are transmitted.
 6. The device of claim 5, wherein the number ofthe at least one idle subchannel is 1, 2 or 4 when the number of theplurality of subchannels is
 4. 7. The device of claim 5, wherein thenumber of the at least one idle subchannel is 1 or 2 when the number ofthe plurality of subchannels is
 2. 8. The device of claim 5, wherein thedevice is a Very High Throughput (VHT) non-Access Point (AP) station andthe station which transmits the at least one CTS frame is a VHT APstation.
 9. A method for receiving data in a wireless communicationsystem, the method comprising: receiving, by a first station, aplurality of request to send (RTS) frames from a second station througha plurality of subchannels, each of the plurality of RTS frames beingreceived through a corresponding one of the plurality of subchannels,each of the plurality of subchannels having a 20 megahertz (MHz)bandwidth; transmitting, by the first station, at least one clear tosend (CTS) frame in response to at least one of the plurality of RTSframes to the second station through at least one idle subchannel of theplurality of subchannels; and receiving, by the first station, a dataframe from the second station after transmitting the at least one CTSframe, wherein each of the plurality of RTS frames includes firstchannel information related to the plurality of subchannels, wherein theat least one CTS frame includes second channel information related tothe at least one idle subchannel through which the at least one CTSframe is transmitted by the first station and the data frame is receivedthrough the at least one idle subchannel indicated by the second channelinformation, and wherein a number of the at least one idle subchannelthrough which the at least one CTS frame is transmitted is equal to orless than a number of the plurality of subchannels through which theplurality of RTS frames are received.
 10. The method of claim 9, whereinthe number of the at least one idle subchannel is 1, 2 or 4 when thenumber of the plurality of subchannels is
 4. 11. The method of claim 9,wherein the number of the at least one idle subchannel is 1 or 2 whenthe number of the plurality of subchannels is
 2. 12. The method of claim9, wherein the first station is a Very High Throughput (VHT) non-AccessPoint (AP) station and the second station is a VHT AP station.
 13. Adevice comprising: a transceiver; and a processor operatively connectedto the transceiver and configured to: instruct the transceiver toreceive a plurality of request to send (RTS) frames from a stationthrough a plurality of subchannels, each of the plurality of RTS framesbeing received through a corresponding one of the plurality ofsubchannels, each of the plurality of subchannels having a 20 megahertz(MHz) bandwidth, instruct the transceiver to transmit at least one clearto send (CTS) frame in response to at least one of the plurality of RTSframes to the station through at least one idle subchannel of theplurality of subchannels, and instruct the transceiver to receive a dataframe from the station after transmitting the at least one CTS frame,wherein each of the plurality of RTS frames includes first channelinformation related to the plurality of subchannels, wherein the atleast one CTS frame includes second channel information related to theat least one idle subchannel through which the at least one CTS frame istransmitted by the device and the data frame is received through the atleast one idle subchannel indicated by the second channel information,and wherein a number of the at least one idle subchannel through whichthe at least one CTS frame is transmitted is equal to or less than anumber of the plurality of subchannels through which the plurality ofRTS frames are received.
 14. The device of claim 13, wherein the numberof the at least one idle subchannel is 1, 2 or 4 when the number of theplurality of subchannels is
 4. 15. The device of claim 13, wherein thenumber of the at least one idle subchannel is 1 or 2 when the number ofthe plurality of subchannels is
 2. 16. The device of claim 13, whereinthe device is a Very High Throughput (VHT) non-Access Point (AP) stationand the station which receives the at least one CTS frame is a VHT APstation.